rsync 2.5.6 security advisory

The rsync team has received evidence that a vulnerability in rsync was recently used in combination with a Linux kernel vulnerability to compromise the security of a public rsync server. While the forensic evidence we have is incomplete, we have pieced together the most likely way that this attack was conducted and we are releasing this advisory as a result of our investigations to date.

Our conclusions are that:

rsync version 2.5.6 and earlier contains a heap overflow vulnerability that can be used to remotely run arbitrary code. While this heap overflow vulnerability could not be used by itself to obtain root access on a rsync server, it could be used in combination with the recently announced brk vulnerability in the Linux kernel to produce a full remote compromise. The server that was compromised was using a non-default rsyncd.conf option "use chroot = no". The use of this option made the attack on the compromised server considerably easier. A successful attack is almost certainly still possible without this option, but it would be much more difficult.